This application describes a 5-year plan to establish an independent career in academic pediatric pulmonology. The candidate's long-term goal is to develop an interdisciplinary research program focusing on microbial pathogenesis in lung infections while maintaining a clinical practice encompassing 20% of the candidate's time. The training environment consists of the laboratory of Dr. Samuel Miller at the University of Washington and the Pulmonary Division at Children's Hospital & Regional Medical Center, both in Seattle. The candidate will expand his research expertise through a project with basic and translational components, augmented by collaboration and advising from senior scientists and clinicians. The formation of bacterial biofilms is associated with antibiotic resistance. One of the best-studied model systems is the chronic Pseudomonas aeruginosa airway infection in people with cystic fibrosis (CF). P. aeruginosa infects CF airways as a biofilm, and it adapts to the CF airway environment during infection. These adaptations affect bacterial responses to antibiotics. Preliminary data demonstrate that P. aeruginosa responds specifically to subinhibitory concentrations of the antibiotic tobramycin with increased biofilm formation. Tobramycin-induced biofilms are more resistant to further antibiotic challenge. Preliminary evidence suggests a role for two cell signaling systems, quorum sensing and the cyclic diguanylate pathway, in the response to tobramycin. Published data led to the hypothesis that responses to tobramycin vary among CF P. aeruginosa isolates, with variable effects on progression of lung disease. We propose to determine the molecular mechanism of the biofilm response of a laboratory strain of P. aeruginosa to tobramycin using available resources (Specific Aim 1). The clinical relevance of this response will then be determined by examining archived clinical isolates from CF patients, as well as environmental strains of P. aeruginosa (Specific Aim 2). The ultimate goal of this project is to identify novel therapeutic targets to inhibit the development of antibiotic resistance, and to aid eradication of chronic infections. The techniques and environments in this proposal are ideal for preparing for a career in the study of lung infections in children.